1. Field of the Invention
The present invention relates to a method for preparing a composite silica membrane with thermal stability by a soaking-rolling method, and more particularly to a method for preparing a composite silica membrane with improved thermal stability by rolling the surface of a porous support with silica xerogel, soaking-rolling the surface with γ-alumina, coating, drying, and sintering the porous support surface, and thereby forming a fine coating membrane on the porous support surface.
2. Description of Related Art
Hydrogen purification using inorganic membranes has drawn much attention of many researchers because it requires a smaller scale than other separation-purification techniques while consuming less energy. There are various methods for preparing inorganic membranes and many different kinds of supports may be used. As supports, alumina, vycor glass, and stainless steel have been used, and alumina support has been most favored.
Conventional methods for preparing inorganic membranes are sol-gel method, chemical vapor deposition, sputtering, electroplating, electroless plating, and the like. Of these, the sol-gel method has attracted much attention due to its simple equipments and process. However, sol-gel inorganic membranes prepared mostly by a dipping method are disadvantageous in that they become unstable at high temperatures. While inorganic membranes prepared by chemical vapor deposition have good thermal stability at high temperatures, sol-gel inorganic membranes have poor thermal stability [Burggraaf, “Fundamentals of Inorganic Membrane Science and Technology” p. 297, Elsevier, NL, 1997]. There was an attempt to prepare inorganic membranes with good separation ability using a material having a high microporosity and a uniform porosity distribution [R. M. de Vos, et al., J. Membr. Sci., 143 (1998) 37-51; B. N. Nair et al., J. Membr. Sci., 135 (1997) 237-243]. However, even if a coating material having good physical properties in terms of microscopic view is used, it cannot exert its full ability if there arises a macroscopic cracking. Similarly, if inorganic membranes prepared by the sol-gel method have cracks on the surface coating membrane due to thermal instability, the separation ability of the membranes will significantly deteriorate no matter how good physical properties the coating material has. If this problem can be solved, sol-gel inorganic membranes will be able to be used in a variety of fields, including high-temperature hydrogen purification and high-temperature membrane reactors.